1. Field of the Invention
The present invention is related to composite materials, and more particularly, to reconfigurable composite materials.
2. Description of Related Art
Conventional structural design typically uses fixed geometry structural elements designed to provide acceptable performance over a range of operating conditions. However, fixed geometry structural elements limit the degree of optimization that can be achieved over the range of operating conditions. Reconfigurable surface technology, which permits structural components to undergo large-scale, in-service changes in component geometry could provide performance enhancements of the structural design over broad operating conditions. Additionally, reconfigurable surface technology could enable a structural design with multi-function capabilities, optimized wave interactions (e.g., electromagnetic, shock, sound, air flow), and improved deployment/storage usability for traveling among others.
Applications that may benefit from reconfigurable surface technology include aircraft wings, control surfaces, and field-deployable structures. Reconfigurable (or morphing) surfaces require large reversible deformations, low parasitic mass, reconfiguration speed appropriate to the application, high degree of shape control and ability to scale to large areas. Morphing or reconfigurable structures potentially allow for previously unattainable performance by permitting several optimized structures to be achieved using a single platform (or structure). New engineered materials (e.g., a composite material) that may achieve the necessary deformations but limit losses in parasitic actuation mass and structural efficiency (stiffness/weight) are needed. These new materials should exhibit precise control of deformation properties and provide high stiffness when exercised through large deformations.
Prior approaches to achieve a reconfigurable or morphing structure such as a morphing airplane wing rely on designs that are relatively mass-inefficient as compared to conventional airframe design. The inefficiency results from the need to use soft, flexible materials such as shape memory polymer matrix composites as the wing skin, forcing structural mass to be concentrated in the interior where it reduces stiffness of the whole structure, as compared to torsion box designs.
Shape memory polymer matrix composites have shown reversible deformation recovery through the combined effect of the energy stored in the reinforcement phase and from the shape memory effect of the polymer. Prior approaches utilize composite fiber reinforcement such as carbon fiber in uni-axial, cross-ply, or woven configurations. The principal challenges in using fibers for these applications are the inextensibility of the fibers, limiting the deformation primarily to bending, and the poor stability of the fiber in compression leading to microbuckling.
Therefore, there is currently much interest in reconfigurable or morphing structures capable of performing large changes in various physical configurations (e.g., a wing or engine inlet) such that optimized performance may be achieved over a broad range of operational conditions. It is desirable to have materials that provide controllable stiffness properties and large deformation. It is also desirable to have materials with attributes suitable for morphing structures such as relatively low in-plane axial stiffness for efficient shape changing, combined with good resistance to out of plane deformations such as those exerted by pressure loading of air or water.